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Or did I just BLOW YOUR FUCKING MIND?!
April 25, 2006 4:09 PM   Subscribe

We've talked about quantum computation a few times before, but how much do we really know? Metafilter, instruct thyself. Don't forget to learn some advanced probability and computational complexity (Scott Aaronson has more). Whoa, that's a lot o' learning, so let's so check out the much easier, and much cooler "sleeping puppy" experiment. I can only dream that will help break quantum mechanics' association with animal abuse. Then, there's the Free Will Theorem that just came out (some discussion on it) and another paper with a new look at an old problem. The latter describes another way of solving ye olde, super importanto Einstein-Podolsky-Rosen paradox using the relational interpretation of quantum mechanics (lots of discussion running around). Whew. We don't need the crackpot ramblings of What the #$*! Do We Know? when we've got real physics to keep us up at night. So, who wants to become a physicist? (t'Hooft has some thoughts for those who want to go theoretical.)
posted by jmhodges (26 comments total) 5 users marked this as a favorite

 
Crap, I forgot Scott's Quantum Computing for High School Students which is a nice introductory piece. Mea culpa.
posted by jmhodges at 4:15 PM on April 25, 2006


I've had lots of trouble grasping quantum computing, and have been hoping in despair that someone will write a "Mr. T Teaches Quantum Computing" comic strip.
posted by rolypolyman at 4:17 PM on April 25, 2006


Holy cow that puppy article is awesome. And no poisoning of juvenile animals or anything.
Excellent post.
posted by Baby_Balrog at 4:34 PM on April 25, 2006


Yeah, the puppy article is pretty cool. And the puppy is so cute!
posted by Orange Goblin at 4:51 PM on April 25, 2006


Scott Arronson is a total dick, and much less intelegent then he thinks he is.
posted by delmoi at 5:02 PM on April 25, 2006


Once the spin of a particle is decided, how long does that decision remain true? Forever? [I'm not talking about the spin of the particle changing, only about the information about the measurement event] Currently our mindset is that once a decision is made, it is true for all time; maybe this is wrongheaded. Quantum erasure shows that quantum information of this sort can be erased as long as it is never leaked into the universe. Extending this idea, can macroscopic parts of the universe be erased? Perhaps the reason why measurements in these experiements always correlate is that when the information is brought together, conflicts are erased. I think that erasure doesnt need to imply a multiverse but only that time be two dimensional. How much do we know about time anyway?

As a tangent, I was thinking about mathematical proofs and time. Is a mathematical idea eternal or does it exist in time? Can it be erased? Consider problems that are undecidable: they cannot be solved by shortcuts, but must be decided by actual computation that may or may not ever complete. If an undecidable algorithm completes to a decision, was the truth of that operation 'true but just not known before the computation completed' or does that truth spring forth at a particular time?

Mathemtatics is a formal system which is written down symbolically in a physical medium. If all information of a mathematical theory were to be erased, is the theory still true or can it 'come out different' next time?
posted by Osmanthus at 5:07 PM on April 25, 2006


For anyone tired of trying to wrap their minds around the different interpretations of quantum mechanics, try John G. Cramer's Transactional Interpretation. Here's a powerpoint slideshow that explains how the transactional interpretation resolves Schrodinger's Cat and other classic paradoxes, and is simple enough that anyone playing with ripples in water can understand it - so long as one thinks of the time dimension as the surface of the water.
posted by Nquire at 5:48 PM on April 25, 2006


Scott Arronson is a total dick, and much less intelegent then he thinks he is.

Please don't make me hurt you. Lie to me. Tell daddy that the typo in question was intentional.
posted by loquacious at 6:13 PM on April 25, 2006


ow! I think my pre-frontal cortex just cramped.
posted by Parannoyed at 6:15 PM on April 25, 2006


Great post. I love this stuff, and have been listening to some lectures on it recently.

The puppy thing left me a bit cold, though. It seems clumsy to me to use macro-level metaphors like these (salad? steak?) to talk about probabilistic quantum states.

much less intelegent then he thinks he is

This is funny. [/spelling nazi]
posted by stavrosthewonderchicken at 6:22 PM on April 25, 2006


Whoops. loquacious beat me to the snark.
posted by stavrosthewonderchicken at 6:22 PM on April 25, 2006


This makes me love being a physics major. Thanks!
posted by Loto at 7:55 PM on April 25, 2006


Please don't make me hurt you. Lie to me. Tell daddy that the typo in question was intentional.

Lol, of course it was, of course it was.
posted by delmoi at 8:02 PM on April 25, 2006


Nope, didn't blow my mind.... I am a theoretical physicist though.

Nice post though, the condescension in the fpp irked me a bit.
posted by ozomatli at 9:32 PM on April 25, 2006


I'm not sure what you thought was condescending in the post. I posted the difficult links first because I wanted people to get a glimpse of what the field "really" looks like (esp. those with an interest) only to follow these links with "reach out" pages to keep the interest of those who aren't going to sit around for the derivation of IP=PSPACE. Most people only get a chance to see the latter and giving them the opportunity to poke at the hard stuff is pretty novel. This post wasn't made "for" theoretical physicists and the last two lines should have made that clear.

Plus, the "blow your mind" bit was me being sarcastic. Specifically, I was thinking about a joke in the Daily Show's America textbook ("If pro is the opposite of con, what's the opposite of progress? Congress. Or did I just blow your mind?"). Everybody does a Keanu Reeves "Whoa" when they learn this stuff and physicists keep doing it or their research and teaching becomes lame. To paraphrase someone smarter than I: if quantum mechanics doesn't blow your mind, you don't understand quantum mechanics.
posted by jmhodges at 9:55 PM on April 25, 2006


Don't worry about it. I am in a cranky mood because my apartment has been invaded by bees.

I encourage everyone to be informed about modern physics, but my experience (and email inbox full) with crackpots who just read some pop-sci book on quantum mechanics tends to make me a bit more cynical than I should be. I really don't think it is possible to have a deep understanding of QM without doing the math. I recommend Griffith's Intro to Quantum book to anyone who wants to learn about QM. All of the flash demos and pop-sci books can never replace actually getting into and playing with Schrodinger's EQ.

Again, sorry about the negative tone of my first post.
posted by ozomatli at 10:04 PM on April 25, 2006


Not a problem, didn't mean to come off as snippy but I did. Also, I second your recommendation of Griffiths'. That thing will be on the shelf of Easy Reaching for years to come, if only to lend it out.
posted by jmhodges at 10:35 PM on April 25, 2006


I read the puppy article. I still don't get it. :P
posted by VirtualWolf at 10:44 PM on April 25, 2006


I don't get it either. Sleeping puppies are piss-poor salad-detection devices.

ISTM that unless either (a) you wake a puppy (b) no puppy-waking occurs despite strong provocation, you can't reliably say whether there's a puppy in there. I can't see how waving very-probably-salad under the nose of a sleeping puppy actually constitutes a measurement of steakhood, even from the assumed puppy's point of view, unless the puppy happens to wake up.

It further STM that there's a necessary tradeoff between the reliability of any such puppy-detection procedure and the total amount of provocation offered to the possible puppy. Didn't Heisenberg once work out something along those lines?

IANATP, obviously.
posted by flabdablet at 6:17 AM on April 26, 2006


yeah but despite it's crackpottery, what the bleep do we know does try to remind people that how you think determines how you act - and that you can change the way you think. which is a good message.
posted by 6am at 6:17 AM on April 26, 2006


Oh, and thanks for the t'Hooft link. That's gonna keep me busy for a while :^)
posted by flabdablet at 6:18 AM on April 26, 2006


I must second Ozomatli's recommendation. Griffith's QM is a really excellent text.
posted by Farengast at 1:36 PM on April 26, 2006


Doesn’t blow my mind, (gut maybe), I love this stuff.
As a Taoist, non-destructive quantum measurement makes total sense to me. I get it.

....crap, I just blew it.

“I can't see how waving very-probably-salad under the nose of a sleeping puppy actually constitutes a measurement of steakhood, even from the assumed puppy's point of view, unless the puppy happens to wake up.”

flabdablet, I suspect they’re measuring functions of bits which describe the superpositions of the puppy, steak, salad, etc, not the bits themselves. Ergo, no full puppy waking required. You’re sliding calculations under the curve of possibility, we and the puppy leave the salad/steak in it’s superpositional state.

Kinda reminds me of the Monty Hall three door thing in terms of counter-intuitiveness.
posted by Smedleyman at 10:41 AM on April 27, 2006


Way cool post btw jmhodges
posted by Smedleyman at 10:42 AM on April 27, 2006


Kinda reminds me of the Monty Hall three door thing in terms of counter-intuitiveness.

Very astute. The solution to both problems depends on recognizing the partial information available to the observer, which is inextricable from the process that led to the observation.

Consider this variant of the Monty Hall problem:

Right after you picka door, but before Monty opens a door, there is an earthquake, and one of the other doors flies open, revealing no prize inside.

"Oh well" says Monty. "Just pick from the remaining two doors."

Should you switch doors?

At first blush, this is the exact same problem, but the process which led to the state of knowledge is different and it does affect the answer.
posted by sonofsamiam at 10:50 AM on April 27, 2006


Bell's Inequalities --what does it mean that there are no "hidden variables"?
Quantum Mysteries Disentangled --what is the connection between "entanglement" and "observation"?
posted by sonofsamiam at 10:55 AM on April 27, 2006


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